A major cost in separating a feed into product by distillation is the capital cost of distillation columns. In the conventional cryogenic distillation of feed air to produce product nitrogen, product oxygen and product crude argon, three columns are used: a first column operating at a higher pressure wherein a preliminary separation is made, a second column operating at a lower pressure wherein product nitrogen and oxygen are made, and a third column wherein product crude argon is produced.
It is desirable to have a distillation system which can produce three products using only two columns as this would significantly reduce the capital cost of the distillation system. In the case of cryogenic air separation, it is desirable to be able to produce crude argon directly from the lower pressure column thus avoiding the need for a third column.
Accordingly, it is an object of this invention to provide a distillation column system comprising two columns wherein a product may be produced from an intermediate point of the second column as well as from the upper and lower portions of the second column.
It is another object of this invention to provide a cryogenic rectification method for processing feed air wherein crude argon is produced while employing only two columns.